It is known that gallium-alkyl compounds, especially those with small alkyl radicals, play an important role in the production of III/V semiconductors, in particular those made of gallium arsenide and gallium phosphide, which are increasingly being used in the realms of electronics and solar technology. Up until now, the production of these gallium-alkyl compounds with the needed degree to purity and in the necessary amounts has posed tremendous difficulties.
Although it is known that gallium-halogen compounds can be alkylated by means of Grignard reagents, this entails a major disadvantage in that the only agent that can be used as the solvent, namely, ether, forms stable adducts with the gallium trialkyl produced. The separation of the adducts causes great problems and it is often accompanied by partial thermal decomposition and impurities in the desired gallium alkyls. The same problem arises in connection with a variant of the Grignard reaction, namely, the reaction of a (optionally metal-doped) magnesium-gallium alloy with alkyl halogenides. In the case of small alkyl radicals, alkylation with alkyl-lithium compounds or alkyl-sodium compounds can also only be carried out in the presence of these solvents which are disadvantageous because of their coordinating effect.
Even though the use of liquid metal alkyls circumvents the problems associated with the subsequent removal of the solvents, in this case, the reaction of gallium halogenides with trialkyl aluminum only allows for high yields if the amounts of this alkylating agent used are well above the stoichiometric level, while it is possible to make use of only one of the three alkyl groups. The reaction of dialkyl mercury for purposes of transferring alkyl groups. The reaction of dialkyl mercury for purposes of transferring alkyl groups to gallium, even with HgCl.sub.2 catalysis, is extremely slow, and the extreme toxicity of dialkyl-mercury compounds prohibits a wider application range. Finally, the dialkyl-zinc compounds, which are also used for the alkylation of gallium-halogenide compounds, are difficult to obtain as initial products.
The known Wurtz synthesis of the simultaneous reaction of alkyl halogenides and metal halogenides in the presence of sodium is very poorly suited to produce gallium-alkyl compounds, not only because two alkyl groups react to form higher hydrocarbons and give rise to impurities, but primarily because the gallium-alkyl compounds, not only because two alkyl groups react to form higher hydrocarbons and give rise to impurities, but primarily because the gallium halogenides employed are reduced to gallium metal. The same also applies to reactions analogous to Wurtz's with halogen acceptor metals other than sodium such as, for example, metals of main groups I to III of the periodical table, which have already been studied as solvents in organic solvents and salt melts. Moreover, the latter are restricted to the methylation of just a few electropositive elements due to secondary reactions of higher alkyl halogenides. For the state of the art, reference is made to West German patent no. 1,239,687, East German patent no. 231,568 and British laid-open application no. 2,123,432.